Scarce spectrum and growing customer demand for faster data throughput are challenges perceived by almost all mobile operators. The existing approaches squeeze the spectrum by enhanced spectrum efficiency algorithms like higher order modulation, but it implies big impact on existing network and handsets, so that in most cases new and expensive hardware has to be introduced.
On the other hand there is already a GSM feature standardised in 3GPP which addresses higher throughput needs without hardware impact at all in the network: downlink dual carrier (DLDC). With DLDC the mobile station is able to receive data over 2 frequencies simultaneously instead of only 1, so that the data rate is doubled.
Dual carrier allows to double the number of timeslots per user and hence the throughput. A description of dual carrier can be found including the 3GPP specification in 3GPP 45.912 Chapter 7.
In GSM data connections, number of timeslots allocated per user is defined in the terminal class, which defines the maximum number of timeslots in downlink (DL), uplink (UL) and DL&UL. Although it is possible to have non adjacent timeslots for data it is hardly limited by the terminal capability (i.e., if a terminal supports 4 timeslots in downlink, it will be able to have at the same time timeslot 7 and 4 as timeslot separation is 4, but not timeslots 7 and 3).
However, in order to be able to use the DLDC capability, several timeslots in different TRXs (transceivers) need to be empty at the same time (i.e. if a cell has 4 TRX there must be at least two TRXs empty within the range of timeslots supported by the mobile). This solution enables to allocate voice resources so empty resources can be used for DLDC.
In order to comply with both the scarce spectrum in one band and the customer demand for faster data throughput, the DLDC feature with a simple but ingenious addition is taken into account. DLDC will use timeslots in different TRXs that are empty at the same time. In order to have that situation as many times as possible the algorithm will allocate voice traffic in contiguous timeslots.
BSC (Base Station Controller) will monitor every x seconds the status of the different timeslots used for voice calls. Voice calls will be located either on the low or high timeslots, and data calls will be located in the other side, e.g. Timeslot 0 has highest priority for voice calls but lowest for EDGE evolution calls. BSC will check if there are empty timeslots with higher priority for voice calls than the ones being used. If that is the case, those voice calls will be moved to the empty timeslots. This will free timeslots in different TRXs that can be used together with DLDC feature.
It is well-known that abbreviations and acronyms are frequently used in the mobile telephony field. Below is a glossary of acronyms/terms used throughout the present specification:
3GPPThe 3rd Generation Partnership ProjectBCCHBroadcast Control ChannelBSCBase Station ControllerBTSBase Transceiver StationDLDownlinkDLDCDownlink Dual CarrierGSMGlobal System for Mobile CommunicationsUPUplinkTRXTransceiver